Seismic exploration involves generating seismic waves at or adjacent the surface of the earth, portions of which waves travel downwardly through the earth and are reflected from interfaces back to the earth's surface. Geophones sense the reflected waves at points spaced from the seismic source. Many geophones include a single motion-sensing transducer responsive only to the vertical component of the received seismic waves. Transducer outputs from an array of such single-transducer geophones often are electrically connected in series circuit, with the output from the series-connected transducers being supplied to one data channel of a multiple-channel recording device for recording of the composite signal from the geophone array. Generally, a plurality of geophone arrays are included at different distances from the seismic source to obtain a plurality of seismic records from groups of geophones. By employing arrays of series-connected or series-parallel connected geophones, the geophone response to Rayleigh, or ground roll, waves, which contain no deep-earth information, is substantially cancelled from the composite seismic records. The outputs from, say, thirty-six geophones may be connected together in an effort to eliminate the Rayleigh wave component from the composite signals. Often, up to one thousand groups, or arrays, of geophones are included in a single set-up. Obvious disadvantages in the use of such prior art arrangements is the need for a large number of geophones, and the time and effort in properly locating and interconnecting the same. U.S. Pat. No. 3,719,924 is illustrative of such prior art method.
Geophones containing three orthogonally oriented transducers are known as shown, for example, in U.S. Pat. No. 3,344,881, White, 3,872,478, Lucole and 4,783,770, Danbom, which transducers may be positioned to individually respond to vertical, horizontal in-line, and horizontal cross-line components of seismic waves. In the White patent, the three transducer outputs are sent over separate transmission paths, such as a plurality of dual-conductor lines, to a multichannel recorder for recording at separate recording channels. These recorded signals may be played back and processed to suppress Rayleigh wave component response, or the like.
As is well understood, the three orthogonally oriented transducers need not be positioned to individually respond to the vertical, horizontal in-line, and horizontal cross-line components of seismic waves. For example, it is common practice to locate the transducers in a Gal'perin configuration wherein the response axis of each transducer extends at an angle of 54.degree. 23' off of vertical. With such an arrangement the effect of gravity on each transducer is the same.
Geophones containing orthogonal transducer elements and which also include signal processing means for ground roll suppression filtering, signal enhancement, or the like, also are known as shown in U.S. Pat. No. 4,458,341. Using this system, fewer geophones are required to cover the same area as are required using the one-transducer geophones.